Percussion Rock Drilling Bit with More Efficient Flushing

ABSTRACT

A design of crown of drill bit for percussive rock drilling with big “V” shape front flushing grooves, small central “dead” area will reduce the repeatedly crushing of broken rock cuttings. It will not only improve the rate of penetration, but also decrease the hole deviation, as well as the erosion to the outer surface of drive sub and case tube of DTH hammer.

THE APPLICATION AREA

The present disclosure relates to bore holes drilling of an earthformation by top hammer hydraulic drilling and down-the-hole (DTH)drilling with a hammer that is driven by pressurized air or otherfluids.

THE BACKGROUND

The button bit technology was mainly focused on increasing the rate ofpenetration, deviation improvement, better materials and bit skirtdesign since their first introduction. There are not significant changesin the designs to improve the flushing efficiency.

However, the actual rate of penetration is determined by the efficiencyof both impacting and flushing. The broken rock debris should be removedvia flushing medium immediately so buttons will hit fresh solid rocksurface with each impact. Otherwise, a portion of the impact energy willbe consumed by crushing the broken debris, eventually slow down thepenetration.

An example of prior art of design is shown in FIG. 1, the flushing holeslocated at the distance about half of the bit front head radius to thecenter. They are connected via grooves 3 in the front face to the sidegrooves 6 of bit head respectively. The front head grooves 3 havestraight parallel edges and the width of them is about the same as thediameter of flushing hole.

From fluid dynamics, the majority of flushing medium at the bottom of ahole will flow through the grooves 3 in the front face of bit, which arebigger passages therefore have less restriction to flushing medium.Broken rock chips within the areas will be blow away by the flushingmedium immediately. The blowing out force of flushing medium is not ashigh in the areas without flushing grooves because of the restrictionand/or resistance of inserts and bit body steel. Furthermore, the bigrock chips are very likely clamped and/or blocked by the bit front face,inserts and rock surface. They will also block smaller chips. Therefore,the majority of broken rock debris could not be blown away on time. Theyget crushed repeatedly, and then are blown out by flushing medium whenmeet the flushing grooves as the bit rotating.

Moreover, the central area of bit front head is a “dead area”, the areawithin the inner edge of the flushing holes/grooves. There istheoretically no flushing force to blow rock debris out from the area.They get crushed repeatedly.

All of the left over rock cuttings act as a cushion between the bit andsolid rock surface. The “cuttings cushion” prevents the inserts frompenetrating the solid rock. Therefore, large portion of impact energy isconsumed by crushing the cuttings and the rate of penetration is sloweddown; the body steel of bits front face gets worn away fast.

The “cutting cushion” also prevents the buttons of bit from grasping thesolid rock, keeping the drill bit in a floating state. Therefore, bittends to move sidewise if it encounter side force, causing the holes'deviation.

With the prior art of design, the width of the front grooves 3 is smallon the edge of bit head. So the velocity of the flushing medium and thecuttings is very high when moving out of the grooves 3, especially forDTH air hammer. Severe erosion will be created on the behind outersurface of drive sub and hammer case tube.

THE DESCRIPTION OF THE INVENTION

As is shown in FIG. 2 and 3, there is only one insert 4 in the centralarea 5 of the front head of the bit, so that the flushing holes 1 can beclose to the center as much as possible to minimize the central deadarea 5.

The width of front flushing grooves 3 becomes wider towards the edge 7of bit crown forming “V” shape front flushing areas as viewed in thedirection perpendicular to the front face 8. Each of the front grooves 3connects to a side groove 6 respectively, which is in the surface of thecylinder and/or cone of bit crown. The rock debris in the areas can beblown away by flushing medium immediately. The inserts 2 moving intothis area will hit the fresh solid rock surface.

The opening size of groove 3 along edge 7 should be as wide as possibleso the total area of the grooves 3 is much bigger than that of theconventional straight grooves, which means much less re-crushing of therock debris under the bit front face 8. Therefore, more impact energywill be used to break solid rock surface. Also the wider openings willsignificantly reduce the velocity of the out moving flushing medium andthe cuttings, which results in much less erosion on the outer surface ofdrive sub and hammer tube.

1. A crown of rock drill bit for percussion rock drilling, comprising atleast three fluid passages or flushing holes 1 which emerge in thevicinity of the front face 8 of the crown; each flushing hole connectingto a radially extending front groove 3 formed in the front face; theouter end of each front groove connecting to a side groove 6 whichextend axially rearward; wherein each land formed between the groovescarries at least one gauge insert 2 and one front insert
 9. 2. The bitcrown, according to claim 1 has only one button in the central area 5,the area within the inner edge of the flushing holes/grooves of thefront head.
 3. According to claim 1, the shape of each front groove 3,when looking at the bit front face, is “V” shape, the width of the frontgrooves, when measuring across the center of the flushing hole, isbigger than its diameter, getting wider outwards, to minimum 1.3 timeswider towards the outer edge 7 of bit front head.
 4. According to claim3, the sides 3 a and 3 b of front grooves 3, when looking at the bitfront face 8, can be straight and/or curved; the opening width of sidegrooves 6 is the same or bigger than that of front grooves 3.